Method for reducing microbiological contamination

ABSTRACT

A method for reducing microbiological contamination in a closed chamber ( 6 ), formed by at least two interconnected components ( 1, 4 ), by introducing a germicidal medium into the chamber ( 6 ).

The invention relates to a method for reducing microbiological contamination in a closed chamber formed by at least two interconnected components.

In the context of this invention, “microbiological contaminants”, or “germs” for short, shall denote contaminants that are also called bioburden in English and which include bacteria, spores, yeasts, fungi, viruses, etc. In the manufacture of containers, in particular of plastic containers, for food, for cosmetics or for medical purposes, in particular for parenterals or for parenteral nutrition, the microbiological quality of the container or of chambers of the container system prior to their filling and/or use is of fundamental importance. For this purpose, the microbiological contamination has to be reduced. As described in DE 198 12 057 A1, it is state of the art in the manufacture of empty, sealed containers for pharmaceutical purposes to use autoclaving or radiation sterilization to achieve sterility of the empty container interior. To prevent the formation of ozone during radiation sterilization, the container has to be filled with an inert gas such as nitrogen or argon. This process requires container materials that are stable to radiation or sufficiently temperature-stable for autoclaving. Even glass has to be chemically stabilized for this process by adding cerium oxide (EP 0858975 A1). This process is not suitable for container systems in which at least one part of the system already contains a sensitive active substance and its other part is not filled. Such container systems include, for instance, multi-chamber containers such as double-chamber syringes or infusion bottles to which a cap has been attached. Such containers, which are manufactured using the well-known BFS (Blow-Fill-Seal) process, are described in detail in the standard DIN ISO 15759.

For these container systems, the closed, empty, complexly shaped interstice (here briefly referred to as the “chamber”) between the head of a filled infusion bottle and its cap has to be safely sterilized, without adversely affecting the temperature-sensitive filling product, for instance solutions of amino acids, inside the bottle. In such cases, the usual terminal sterilization, which is usually performed by autoclaving at temperatures above 100° C. for standard infusion solutions, such as 0.9% saline solution, is not feasible. Radiation sterilization of the empty chamber using electron beams or gamma radiation would require very complex and expensive shielding measures of the filled container part to prevent damage to the filling product owing to irradiation. The commonly used container materials, such as low-density polyethylene or polypropylene, which have only a low temperature stability, preclude any heat treatment of the empty chamber for the significant reduction of the germ count by heat, e.g. by infrared radiation, laser radiation or similar. Due to the complex geometry of the closed chamber and the resulting dead spot effects, direct irradiation using light or light pulses is generally unsuitable to safely reach all surfaces for reducing the germ count.

With regard to this problem, the invention addresses the problem of specifying a simple and rapid method for significantly reducing the number of microbiological contaminants on the inner surfaces of a microbiologically sealed chamber of complex geometry and small volume, preferably sterilizing this chamber, in particular creating a chamber adjacent to a chamber of the container system filled with a liquid or a solid.

According to the invention, this problem is solved by the method stated in claim 1. Accordingly, the invention provides “chemical sterilization” so to speak, in which a germicidal medium is introduced into the chamber. In the simplest case, the germicidal effect in the chamber is produced by the medium introduced before the chamber is closed, without any additional external supply of energy.

An increased germicidal effect can be achieved if the medium inside the chamber is exposed to the effect of an energy source.

With special advantage, a germicidal fluid can be introduced into the chamber as a medium in a metered manner.

Advantageously, the energy source is used to heat the fluid to at least partially transition from the liquid phase to the gaseous phase.

The energy supply can be used to at least partially vaporize the fluid, resulting in a distribution of fluid and fluid vapors inside the chamber to be sterilized.

A particularly rapid evaporation and uniform distribution of fluid and fluid vapors can be achieved if the energy for heating is introduced in the form of radiation pulses.

Preferably, the energy is supplied and the fluid is selected such that the fluid is at least partially chemically modified or degraded during its residence time in the chamber.

The fluid can be held in the chamber for a residence time, during which the concentration of the fluid or its degradation products can be at least partially reduced by permeation out of the chamber. Preferably, the temporal course of the change of the concentration of the fluid and/or its degradation products in the chamber is tracked using spectroscopic methods. Infrared spectroscopy, in particular laser absorption spectroscopy, is preferably used for this purpose.

The evaporation of the fluid by heating it directly, using dielectric heating without any significant heating of the walls delimiting the chamber, is particularly advantageous. To this end, radio waves in the frequency range of 5 MHz to 50 MHz can be used or microwaves can be used for dielectric heating, wherein a frequency range from 500 MHz to 30 GHz can be provided for, preferably frequencies of 950 MHz or 2450 MHz or 5800 MHz. Direct dielectric heating of the fluid permits its direct evaporation and immediately subsequent condensation on the colder walls that define the chamber. This process (evaporation, distribution and recondensation) can then be repeated systematically using further radiation pulses.

With particular advantage, an aqueous and/or alcoholic solution containing chlorine, ozone and/or a peroxide, preferably hydrogen peroxide, is provided as the fluid. These solutions can easily be directly heated and evaporated by means of microwave radiation; during the process solutions containing ozone or hydrogen peroxide are chemically degraded to the harmless substances water and oxygen.

Likewise, an antiseptic can be used as a fluid, preferably containing at least one active alcoholic substance, particularly preferably ethanol and/or isopropanol.

The components forming the chamber can be a cap and the head of a container, preferably a container for medical purposes. The components can be formed essentially from at least one plastic, preferably from polyolefins, particularly preferably polypropylene or low-density polyethylene. Radio or microwave radiation does not heat these materials or only very slightly, so that they provide well suited condensation surfaces for fluid vapors.

The respective filled container may advantageously be manufactured using the BFS process and the filled container may have a head membrane having at least one depression. Such containers, which may be manufactured by coextrusion and having multiple layers, may be formed as shown in DE 10 2013 012 809 A1.

The invention is explained in detail with reference to the drawings below. In the drawings:

FIG. 1 shows a perspective oblique view of a partial representation of a state-of-the-art infusion container, to the neck collar of which a cap can be attached;

FIG. 2 shows a simplified longitudinal section of a cap that can be attached to the container of FIG. 1; and

FIG. 3 shows in simplified longitudinal section the neck collar of the container of FIG. 1 with the cap of FIG. 2 attached.

The method of chemical sterilization according to the invention is explained with reference to the attached drawing, using an infusion bottle made of plastic having a tightly attached plastic cap and manufactured according to the BFS process known per se by way of example, wherein an aqueous is hydrogen peroxide solution is provided as the germicidal medium. In a analogous way, the invention can also be applied to other container systems mentioned above and using other solvents, germicidal agents, such as known disinfectants (antiseptics), which are also mentioned above. The container denoted by the numeral 1 and shown in FIG. 1, which is manufactured and filled according to the BFS process, has a neck collar 2 at the container neck 3 and above it a head membrane 8 forming the tight container closure and which can be perforated for an infusion process, as described in DIN ISO 15759.

FIG. 2 shows a cap 4, made of a rigid plastic material and also is formed according to DIN ISO 15759 and, as shown in FIG. 3, that can be tightly welded to the neck collar 2 of the container 1 at the cap edge along a welding point 7, for instance by means of hot plate welding. The cap 4 could also be tightly connected to the container 1 by over molding. As shown in FIGS. 2 and 3, elastomeric elements 5 sealing the system during use are located at the opening areas of the top of the cap 4 at points that can be pierced by a cannula or spike for an infusion procedure. The elastomeric elements 5 are, as described for instance in the application DE 10 2017 000 048.4, which shows a post-published state of the art, made of an elastomer, which is suitable for being cohesively welded to the material of the cap 4. FIG. 3 shows a chamber 6 closed up in a sealed manner in the cap 4, when the latter is connected to the neck collar 2, which chamber extends along the inside of the circular cylindrical side wall 10 of the cap 4 and along the head membrane 8 and forms an interstice of relatively small volume, which is chemically sterilized by the method according to the invention.

For this purpose, in the example of the method to be described here, a small volume (approx. 0.01 ml to 0.3 ml) of an aqueous hydrogen peroxide solution is metered onto the head membrane 8, for instance by dropping or spraying, and then the cap 8 is sealingly connected to the neck collar 2 so that the chamber 6 is closed in a sealed manner. Alternatively, the fluid can also be sprayed onto the inner surfaces of the cap 4. Direct heating of the applied fluid is achieved by microwave radiation. This has the advantage of heating the fluid directly, while the walls of chamber 6 are warmed only slightly, if at all, such that the radiation itself contributes only indirectly to the reduction of the germ count. At a preferred frequency of microwave radiation in a frequency range of 500 MHz to 30 GHz, the fluid is at least partially evaporated and thus distributed homogeneously inside the chamber 6. Due to the increase in volume during evaporation, this results in an overpressure in chamber 6 and thus to the pressure-induced overheating of the hydrogen peroxide. On the one hand, this initiates the chemical decomposition of the hydrogen peroxide into the harmless substances water and oxygen, on the other hand, even surfaces that are difficult to access, such as undercuts, gaps, channels and the like, are reliably reached.

Advantageously, microwave pulses are used, which result in a pulsating continuous, at least partial evaporation and repeated micro-condensation of the hydrogen peroxide, a preferred type of condensation, in which extremely small droplets, not visible to the naked eye, are generated. This is also where the thermal break-down of the hydrogen peroxide to water and oxygen sets in. In contrast thereto, in the known methods of sterilizing insulators using gaseous hydrogen peroxide, care must be taken to prevent break-down from occurring in the vaporizer.

An advantage of the method according to the invention is also no carrier gas being required to transport the gaseous hydrogen peroxide, but generating gaseous hydrogen peroxide directly in the chamber 6 to be sterilized and at least partially degrading it there. It was also found that even sensitive filling products present in the container 1 were not measurably affected. It is assumed that the hydrogen peroxide is already broken-down to a large extent before there is any noticeable permeation into the filling product. Due to the low adsorption and permeation of hydrogen peroxide to and into polyolefins, especially to low-density polyethylenes, such container materials are preferable. As described in DE 103 47 908 A1 for instance, multilayer containers can also be used, whose barrier layers - for example made of ethylene vinyl alcohol copolymer (EVOH) or cycloolefinic components such as cycloolefin copolymers COC (trade name Topas) or cycloolefin polymers COP (trade name Zeonor)—minimize the permeation of the germicidal active substances of the fluid, especially oxygen or alcohols, into the interior of container i but not through the cap 4. It is also advantageous to use container headpieces having depressions in the head membrane, as shown in detail in DE 10 2013 012 809 A1.

An advantage of the procedure according to the invention is the very simple gravimetric or volumetric metering of the fluid via the liquid phase and the fact that the sterilization conditions can be easily adapted to the volume of the chamber 6, to the geometry of the container system and to its germ load via the quantity and concentration of the hydrogen peroxide solution (typically 3%-35%) introduced into the chamber 6, and can be controlled via the duration, the intensity and the pulse shape of the microwave. It has been found that a higher reduction in the number of germs can be achieved by several short-term microwave irradiation cycles than by a few, longer-lasting ones. Furthermore, it has been shown that increased hydrogen peroxide concentrations in the gas phase result advantageously in a reduction in the number of germs and the use of ethanolic-aqueous hydrogen peroxide solutions improves the wetting of the surfaces to be sterilized and thus also increases the germination reduction.

Experiments to prove the germ count reduction were performed by means of bio-indicators using spores of Geobacillus stearothermophilus. 0.02-0.2 ml of 35% aqueous H₂O₂ solution were metered onto the head membranes 8 of filled 250-ml-infusion bottles made of LDPE, the head membranes having different diameters (20-30 mm), and an HDPE cap 4 was welded on the head membranes 8. The volume of the chambers 6 formed in that way was in the range of approximately iml to approximately 3m1 on average. Sterilization experiments were performed using a microwave chamber having an adjustable microwave power of 0.6 KW to 6 KW and an MW transmission frequency of 2450 MHz. The direction of irradiation was parallel to the head membrane 8, i.e. perpendicular to the longitudinal axis of vessel 1. The filled area of vessel 1 was additionally shielded using a close-meshed wire net.

Surprisingly, a significant reduction in the germ count was achieved even in narrow gaps only a few millimeters wide, in particular between the head membrane 8 and the cap 4 and between the vessel head and the cylindrical part 10 of the cap 4. This was all the more successful the more frequently microcondensation occurred, i.e. for an increasing number of irradiation cycles and the resulting pressure pulses.

Moreover, the method in accordance with the invention permits a simple and direct verification of the leak-free application of the infusion cap 4, for instance verification by spectroscopic methods. For this purpose, the content of hydrogen peroxide in the gaseous phase and/or the oxygen content in the chamber 6 can be determined in a non-destructive manner. Laser absorption spectrometers having typical wavelengths in the infrared range between 760 nm and 2000 nm are suitable for this purpose. Alternatively, the concentration of gaseous hydrogen peroxide can be monitored and measured using photo fragmentation laser-induced fluorescence (PF-LIF).

Typically, low power levels are sufficient to generate the microwave pulses, preferably at frequencies of 896 MHz/915 MHz/922 MHz (L band) or 2450 MHz (S band) or 5.8 GHz (C band). When using radio waves (frequency range 5 MHz-50 MHz), more power is required due to the weaker coupling, but there is less interference, which significantly reduces so-called hot spots, which cannot always be avoided when using microwaves. 

1. A method for reducing microbiological contamination in a closed chamber (6), formed by at least two interconnected components (1, 4), by introducing a germicidal medium into the chamber (6).
 2. The method according to claim 1, characterized in that the medium inside the chamber (6) is exposed to the effects of an energy source.
 3. The method according to claim 1, characterized in that a germicidal fluid, preferably in liquid form, is introduced into the chamber (6) as the medium.
 4. The method according to claim 1, characterized in that the fluid at least partially changes from the liquid phase to the gaseous phase, preferably transitions to the gaseous phase due to heating by means of an energy source.
 5. The method according to claim 1, characterized in that the fluid in the chamber (6) is at least partially vaporized and condensed at least once, preferably vaporized and recondensed several times.
 6. The method according to claim 1, characterized in that the energy for heating is introduced in the form of radiation, preferably in the form of radiation pulses.
 7. The method according to claim 1, characterized in that the radiation essentially only directly heats the fluid.
 8. The method according to claim 1, characterized in that the fluid is at least partially chemically modified and/or degraded during its residence time in the chamber (6).
 9. The method according to claim 1, characterized in that the fluid is held in the chamber (6) for a residence time, during which the concentration of the fluid and/or its degradation products can be at least a partially reduced by permeation out of the chamber (6).
 10. The method according to claim 1, characterized in that the course of the change in the concentration of the fluid and/or its degradation products in the chamber (6) is tracked using non-destructive, preferably spectroscopic methods.
 11. The method according to claim 1, characterized in that the fluid is evaporated by means of dielectric heating using radio waves in the frequency range of 5 MHz to 50 MHz.
 12. The method according to claim 1, characterized in that evaporation of the fluid is effected by dielectric heating using microwaves in the frequency range of 500 MHz to 30 GHz, preferably having frequencies of 915 MHz or 2450 MHz or 5800 MHz.
 13. The method according to claim 1, characterized in that a solution containing chlorine, ozone or a peroxide, preferably hydrogen peroxide, is provided as the fluid.
 14. The method according to claim 1, characterized in that a solution containing water and/or at least one alcohol, preferably water and ethanol, as a solvent is provided as the fluid.
 15. The method according to claim 1, characterized in that an antiseptic is provided as the fluid, which preferably contains at least one alcoholic active substance, particularly preferably ethanol and/or isopropanol.
 16. The method according to claim 1, characterized in that a cap (4) and the head (2) of a container (1), preferably a filled container (1) for medical purposes, are provided as the components forming the chamber (6).
 17. The method according to claim 1, characterized in that the components (2, 4) are essentially formed from at least one plastic, preferably polyolefin, particularly preferably polypropylene and/or polyethylene.
 18. The method according to claim 1, characterized in that the filled container (1) is produced using the BFS process.
 19. The method according to claim 1, characterized in that the filled container (1) has a head membrane (8) having at least one depression.
 20. The method according to claim 1, characterized in that the filled container (1) is a multilayer container, preferably having at least one layer containing an ethylene-vinyl alcohol copolymer or a cycloolefin polymer or cycloolefin copolymer. 